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THE PEANUT 

{Arachis hypogea) 



ITS HISTORY, HISTOLOGY, PHYSIOLOGY, 
AND UTILITY 



RALPH AUGUSTUS WALDRON, B.S., M.S. 



'\ 



Thesis Presented to the Faculty of the Graduate School of the University of Penn- 
sylvania, May 1918, in partial fulfilment of the requirements 
for the degree of Doctor of Philosophy. 



PHILADELPHIA, PA. 

1918 



^^^%^ 

^^v 



THE PEANUT {Arachis hypogaea)—\i:^ HISTORY, 
HISTOLOGY, PHYSIOLOGY, AND UTILITY 

BY 

Ralph Augustus Waldron, B.S., M.S. 
With Plates LXXIX and LXXX 

Thesis Presented to the Faculty of the Graduate School of the University of Penn- 
sylvania, May 191 8, in partial fulfilment of the requirements 
for the degree of Doctor of Philosophy. 



CONTENTS 

Introduction 302 

History 302 

Introduction 302 

Early American Records 302 

Lack of Evidence as to its extra-American Origin 305 

Distribution 306 

Recent Literature 310 

General Morphology 310 

Histology 313 

Root i'^Z 

Stem 314 

Leaf 314 

Fruit 315 

Physiology 320 

Root Hairs 320 

Observations and Experiments with Root Hairs 322 

Absorption 325 

Development 325 

Biological Considerations Concerning the Fruit and Gynophore 327 

Conclusions from Physiological Studies 331 

Uses of the Peanut 332 

Summary of Results 335 

Literature Cited 337 

Explanation of Plates 338 



302 WALDRON— THE PEANUT 



Introduction 



Few plants present as great interest or diversity of problems for 
botanical study as the peanut. Agriculturally it is of great import- 
ance as a soil renovator and forage plant. From an economic stand- 
point, its products are of great value, every part of the plant being 
of some direct or indirect use. The peanut, potato, cotton, tobacco 
and Indian corn, — five plants which are exerting great influence in 
the world's commerce and industries — were contributed by the new 
world. The peanut, although still in the background of some of 
these, promises to rival, if not surpass, them in importance. It is 
often grown in the economic house of botanical gardens and as a 
novelty out of doors. After a brief botanical study of the plant from 
the morphological standpoint, certain problems were presented 
which bear an important relation to its physiology, and are rather 
striking in their bearing on some well known ecological problems. 
A study of the history of the plant, and brief discussions concerning 
its economy in nature and its utilization by man, have now been 
taken up in succeeding pages. The writer, in here recording these 
observations, feels that he has made but a beginning and hopes to 
continue investigations in the future. 

The writer wishes to express his grateful appreciation to Professor 
John M. Macfarlane, of the University of Pennsylvania, for his 
many suggestions and kind guidance in working up this treatise. 

History 

Introduction. With few exceptions, authors agree that the ori- 
ginal home of the peanut {Arachis hypogaed) is uncertain. In the 
mind of the writer, there are sufficient facts at hand to state definitely, 
as have one or two already, that it is a native of Brazil, although, 
as with many other extensively cultivated plants, it has never been 
recognized in the truly wild state. There is no evidence to contra- 
dict the view that it is a native of this part of South America. The 
writer gives below a synopsis of his studies regarding the native 
home of the plant and its history so far as known in relation to man. 

Early American Records. The earliest mentions in any existing 
literature are those pertaining to Brazil and Peru, and these ante- 
date any found in European works. Acosta^ in his work published 
in 1598, refers to it along with other plants which are native to 
Brazil, and calls it "mani," a name still applied to it among Spanish 



JUH 25 §• 



WALDRON— THE PEANUT 



303 



speaking people of South America. Monardes", according to 
Marcgraf and Piso^, indicated its presence in Peru about this time, 
giving it the name of "anchic." Aside from these and other early 
mentions in literature, fruits of the plant were found in tombs at 
Ancon, Peru. Their presence there undoubtedly antedates the 
Spanish conquest, and so, also, any written record. According to 
Dubard , it was taken from Brazil to Peru sometime before the 




Figure I (after Marcgraf & Piso). Mundubi Braziliensis. 

sixteenth century and there "was cultivated from an early unknown 
date." Among European works, Parkinson** in his celebrated 
^'Theatrum Botanicum" published in 1640, gives an illustration of 
the fruit, which is very likely the first. A few years later, (1648) 
Marcgraf and Piso were the first to figure the whole plant (Fig. i). 
It seems worth while to quote parts of Parkinson's quaint descrip- 
tion as follows: 

"ArACHUS viroycia AmERICANUS. UNDERGROUND CiCHELING OF 

America or Indian Earthnuts." 
"The Indian Earth-nuts (the figure whereof, I give you together 
as they are termed to us by them that have brought them us) are 



304 WALDRON— THE PEANUT 

very likely to grow from such like plants as are formerly described, 
(Species of Vicia) not onely by the name but by the sight and taste 
of the thing it selfe, for wee have not yet scene the face thereof 
above ground, yet the fruit, or Pease-cods (as I may so call it) is 
farre larger, whose outer huske is thicke and somewhat long, round 
at both ends, or a little hooked at the lower end, of a sullen whitish 
color on the outside, striped, and as it were wrinkled, bunching out 
into two parts, where the two nuts (for they are bigger than any 
Filberd kernell) or Pease doe lie joyning close one unto another, 
being somewhat long, with the roundnesse firme and solide, and of a 
darke reddish colour on the out side, and white within tasting sweet 
like a Nut, but more oily." 

' Concerning the introduction into Europe Parkinson's discussion 
indicates that they were introduced into Portugal. He received 
specimens sent from Candy and Lisbon. To quote him further he 
states that the Indian earthnuts are found in "most places of Am- 
erica, as well as to the South, as West parts thereof, both on the 
Maine and Islands; and generally called by our English Sea-men 
that goe into those parts Earth-nuts, erroneously enough, as they do 
most other things that they there meete with." 

Eight years after Parkinson's reference the plant was described as 
follows by Marcgraf and Piso — "Mundubi Brasiliensis Herba, in 
pedalem aut bipedalem altitudinem adsurgit, caule quadrato aut 
striato, ex viridi ruffescente & piloso. Hinc inde enascuntur ramuli 
primo quasi caulem amplectentes & foliolis angustis, acuminatis 
stipati; mox habent nodum ac trium vel quatuor digitorum longi- 
tudine extenduntur; continetq; quilibet ramulus quatuor folia, 
duo semper sibi opposita paulo plus quam duos digitos longa sesquidi- 
gitum lata superne, laete viridia, instar trifolii, inferne paulum canes- 
centia, nervo conspicuo & subtilibus venulis quasi parallelis dotata, 
raris quoque pilis vestita. Ad exortum ramulorum qui folia gerunt 
prodit pediculus sesquidigitum circiter longus, tenuis, flosculumgerens 
flavum & per oras rubentem duobus foliolis constantem, more vic- 
iorum aut trifolii. Radix illius haud longa, tenuis, contorta, filam- 
entosa, cui adnascuntur folliculi ex albicantegrysei,figura minimae 
cucurbitae, oblongae, magnitudinae Myrobalani fragiles: quilibet 
autem continet in se duos nucleos, pellicula saturate purpurea vestitbs,, 
carne intus alba, oleaginosa, sapore pistaceorum, qui comeduntur 
cocti & inter bellaria aponuntur. Multum tamen comesti capitis 
dolores causare ajunt. Fructu integro quassato nucle intus strep- 
unt" 



WALDRON— THE PEANUT 305 

Linnaeus^ says it inhabits Surinam, Brazil and Peru, but does not 
state whether it is wild or cultivated. 

Lack of Evidence as to its extra-American Origin. Among old world 
literature antedating the i6th century, no mention is made. It 
was thus unknown there before the discovery of the new world. 
According to Watt^, all Greek, Latin, Bengalese and Arabian writers 
are silent concerning the plant. This is very significant since the 
peanut is too valuable a plant to have been known to Sanskrit 
speaking peoples and not be used by them. Such a plant could 
hardly have an antiquity among them without some record being 
kept. Until quite recently a mention by Theophrastus of an Egyp- 
tian grown plant was thought by some, to be a reference to Arachis, 
but this has since been disproved. If it had ever existed in Egypt 
it could still be found there. Furthermore no mention is made of it 
in the works of Forskal^ or Delile^. It is not recorded by any 
early writer on the flora of India. According to De CandoUe^'' in 
Dr. Bretschneider's study of Chinese works , the statement is 
made that its introduction into that country was in the sixteenth 
century. It is not mentioned in ancient Chinese literature. This 
suggests the possibility of its introduction there from Peru by such 
expeditions as Magellan's. 

De CandoUe states: "The antiquity of its cultivation in Africa 
is an argument of some force which compensates to a certain degree 
its antiquity in Brazil." The only points offered to indicate an 
African antiquity are (i) the statement by Sloane^^ that it was 
used as food on the early slave ships sailing between Africa and 
America, and (2) that it now has a wide area of cultivation there, 
both of which could very readily 'have occurred after its introduction 
from Brazil. The writer would suggest that the very earliest ships 
to sail from Brazil to Africa took s,tt(\s oi Arachis to that place, and 
the environment of the west coast being ideal for its growth, its 
cultivation very early became widespread; and this has, during the 
last century, developed into a great industry in the French colonies. 

Pison, in his early Brazilian work figures a somewhat similar plant, 
in its habit of fruit production, to Arachis, but states it to be African, 
while he says Arachis is Brazilian. This was a species of Voand^.eia. 
To quote De Candolle again, he states, "the silence of Greek, Latin 
and Arab authors, and the absence of the species in Egypt at Fors- 
kal's time lead me to think that its cultivation in Guinea, Senegal, 
and the east coast of Africa is not of very ancient date; neither has 



306 WALDRON— THE PEANUT 

it the marks of a great antiquity in Asia. No Sanskrit name for it 
is known, but only a Hindustani one. Rumphius^^ says that it 
was imported from Japan to several islands of the Indian Archipelago. 
It would in that case have borne only foreign names, like the Chinese 
name, for instance, which signified "earth bean." At the end of the 
last century (19th) it was generally cultivated in China and Cochin- 
China. Yet, in spite of Rumphius's theory of an introduction into 
the islands from China or Japan, I see that Thunberg does not 
speak of it in his Japanese Flora. Now, Japan has had dealings 
with China for sixteen centuries, and cultivated plants, natives of 
one of the two countries, were commonly early introduced into the 
other. It is not mentioned by Forster among the plants employed 
in the small islands of the Pacific. All these facts point to an Am- 
erican origin." No authors speak of it v/ild or uncultivated in either 
hemisphere. Those who speak of it in Asia or Africa carefully say 
it is cultivated. Piso, in writing of Brazil, says the species is planted. 
Marcgraf does not mention it as cultivated, indicating however 
that it may have been. As to foreign names such as the Chinese, 
meaning "earth-bean," they are all such as would occur to any one 
upon seeing the plant. Contrary, therefore, to the suggestion of 
some authors, little significance need be attached to the American 
names not having accompanied it in its travels to Japan and the 
Orient. 

According to Watt, Sir George Birdwood in his Bombay products 
gave it a Sanskrit name meaning earth-gram. This name has been 
repeated by some subsequent writers without the authenticity of 
it being inquired into. 

Distribution. According to Behtham^^ in "Flora Brasiliensis," 
there are seven species of Arachis found in Brazil, six of which are 
found in the wild state. The other {A. hypogaed) he states is generally 
cultivated in all warm parts of the world. Now, De Candolle well 
remarks in this relation that: "A genus of which all the well known 
species are thus placed in a single region of America can scarcely 
have a species common to both hemispheres; it would be too great 
an exception to the law of geographical botany." By referring to the 
accompanying outline map (Figure 2) which shows the reported 
distribution of these species it will be noted that A. prostrata is the 
most widespread, and A. pusilla the most restricted of the group. 

The writer asks if varieties of this plant, so generally grown in 
such environment as exists in Brazil, may not be cultivated forms of 
one or more Brazilian species? 



WALDRON— THE PEANUT 307 

Of the several cultivated varieties grown today there are recog- 
nized two general types of plants as follows: (i) The bunch type, 
growing erect and bearing its fruit around the base of a single stem. 
The Spanish variety is an example. It can withstand considerable 
moisture conditions and its erectness suggests a shade loving ten- 
dency. (2) The trailing type, with its several branches spread on 
the soil, succeeds best in a hot sandy soil, indicating greater xero- 
phytic tendencies. The Jumbo variety is an example. Now, the 
wild Brazilian species A. pusilla, is an erect .plant, simulating the 




Figure 2 
Outline Map of Brazil indicating the reported distribu- 
tion of the different species of Arachis. 
I. A. pusilla. 
1. A. prostrata. 

3. A. vi/Iosa. 

4. A. glabrata. 

5. A. marginata. 

6. A. tuberosa. 

bunch variety and is reported as growing in dry woods and shady 
places. Another, A. prostrata^ is more trailing and grows in open 
sandy places and so, sifnulating the prostrate cultivated variety, is 



308 



WALDRON— THE PEANUT 



more xerophytic. Thus the possibility is suggested, first, that the cul- 
tivated bunch varieties are derived from such a species as A. pusilla 
and second, that the prostrate varieties are derived from A. pro strata. 
Other evidence in support of this theory is seen in the marked differ- 
ence in the histology of the fruits of the two domesticated varieties. 




7 






'wm^'^w 



9 







Figure 3 (after Dubard) 




Ty 


pes 


of peanuts taken at random from 






I. 


Tombs at Ancon, 


Peru. 






2. 


Java. 








3- 


Tonkin. 








4- 


Madagascar. 








5- 


Madagascar. 








6. 


Spain. 








7- 


Dahomey. 








8. 


Senegal. 








9- 


Spain. 





The following summary taken from Dubard further indicates the 
possibility of our present day varieties being derived from two such 
wild plants. He states that there were two types of peanuts dis- 
tributed over the world from South America; one being a two- 
seeded Brazilian type and the other a three-seeded Peruvian type. 
The first form was carried to West Africa by Portuguese negroes, 



WALDRON— THE PEANUT 309 

according to this author. It was taken to Europe by early travelers,, 
the Portuguese being there the first propagators, as indicated by 
Parkinson and others. Further evidence in support of this east- 
ward distribution, which seems more natural from the geographical 
standpoint, is, that (i) all early illustrations of European and 
Brazilian works show two seeds, and (2) those of West Africa are 
two-seeded. The Peruvian type was a variety created in Peru from 
a form carried there from Brazil some time before the sixteenth cen- 
tury. The question now arises as to the possibility of this plant 
being a different species from the common two-seeded type. Ben- 
tham states the number of seeds to vary from one to three in this 
genus. This being true, any species might well have been selected. 
However, Dubard later describes differences in the structure of 
these which are sufficiently marked to separate them into species. 
About Magellan's time, this three-seeded form was carried from Peru, to 
the Moluccas, Phillipines, Indo-China, Asia and Madagascar. If this 
is true, we should find the three-seeded fruits in these Pacific local- 
ities, and this Dubard proves to be true, by comparing specimens 
taken at hazard from Java, Indo-China and Madagascar. (Figure 3.) 

Finally, if peanuts of to-day from Spain and North America be 
examined, the above two types will be found, indicating a meeting 
again of these, after having been carried around the world in opposite 
directions, yet remaining distinct in character. The Peruvian form 
was undoubtedly carried north and east, but at a date much later 
than its westward spread. The supposition, according to record, 
that the two were present at about the same time, — the one in Africa 
and Europe, the other in the Orient, — further supports this view. 
Watt states that one name given it in India, where it is much culti- 
vated, is "Manilla-Kottai." This suggests its introduction there 
from the Phillipines. All these facts relating to the distribution 
are suggestive, when the lack of evidence of its presence during ancient 
times in China, India, Africa and Europe is considered. 

Since Dubard does not describe the plants of his two forms, it is 
impossible to determine whether or not they might correspond to 
the erect and prostrate types. He does describe the fruit and seed 
of each, however, and it is found that his Brazilian form corresponds 
to some of the erect, and his Peruvian form to some of the prostrate 
varieties of to-day. If such a history is possible, which does not 
seem unlikely, the reported distribution of the two wild species — 
A. prostrata and A. pusilla — is again significant. The former, 



310 WALDRON— THE PEANUT 

found In all parts of Brazil, would be the one most naturally carried 
to Peru rather than the more restricted latter species that is found 
only in the eastern part. The lack of full descriptive literature on 
the distribution and morphology of wild and cultivated varieties 
opens up opportunities for further investigation. 

To-day, varieties are rapidly being increased in number by man. 
This fact, with the ease of intercourse between different countries, 
explains in part at least why there are such varieties as the Virginian, 
Spanish, African, Asiatic, etc. It does not indicate in any way the 
native home of the peanut, which is undoubtedly Brazil. 

Recent Literature. During the last 25 years most of the literature 
on the peanut has been largely concerned with either its culture, uses 
or chemistry. The writer does not attempt to summarize these and 
includes titles of but a few of the more recent publications in his 
bibliography. By referring to the Experiment Station Record of 
the United States Department of Agriculture, many such references 
may be found. During the past few years, publications concerning 
its culture and varieties have been issued by several of the Agri- 
cultural Experiment Stations of those southern states in which the 
peanut is becoming an important crop. 

Concerning the study of the plant from a morphological stand- 
point, little has been done. In 1895, Pettit^^ worked on the fruit 
stalk. She described its structure in detail and discussed its phys- 
iological relation to the plant. 

Winton^^ published the results of a histological study of the 
mature fruit, undertaken especially to secure data for use in the 
microscopical examination of peanut products. In this relation he 
described and illustrated the cell structure of the fruit, testa and 
cotyledons. Adam^^ in 1908 published a fine work concerning its 
history, growth habits, varieties, culture, products and industry in 
western Africa. 

General Morphology 

Description. Since there are two well recognized forms of the 
peanut plant, the author suggests a division of the Linnaean species 
into the two sub-species — (i) fastigiata for the bunch type, and (2) 
procumbens for the prostrate type, and including under each a num- 
ber of varieties. Adam gives the full species name asiatica for the 
former, and ajricana for the latter. Such are not only names of 
varieties and localities, but suggest an erroneous origin. The fol- 



WALDRON— THE PEANUT 311 

lowing is a description of the species, the suggested sub-species and 
the common varieties. 

Arachis hypogaea 
Family Leguminosae Sub-family Hedysareae 

An herbaceous annual. 

Roots — fibrous, delicate and white when young. Root hairs 
usually in rosettes at the base of the side roots — rarely with normal 
tip hairs. Nodules spherical; surface gray, interior pink; appear- 
ing when plants are 8-10 weeks old. 

Hypocotyl — 2-8 cm. long, sometimes slightly swollen at base dur- 
ing germination. 

Ste7ns^-i,o-%o cm. long, erect, or prostrate, more or less hairy, 
tough, flexible, slightly quandrangular. Main stem usually branch- 
ing early into cotyledonary branches. 

Cotyledons — low epigeal, green, with short, thick petiole; remain- 
ing fleshy for two to three weeks, when they dry and drop ofi^. 

Leaves — sensitive to light, 8-12 cm. long, alternate, stipulate, 
pinnately compound. Stipules linear-lanceolate, erect, striate. Pet- 
iole straight, firm, with a single groove along the upper side; a pulvinus 
at its base. Leaflets 2-5 cm. long, four in two pairs, oblong to obo- 
vate; apex rotund and tipped by a tiny spine; veins pinnately 
arranged; under surface slightly hairy; each attached to the petiole 
by a short pulvinus which causes them to close together vertically 
in pairs at night. 

Inflorescence — an axillary, usually three flowered, fascicled and 
reduced head. 

Flowers — yellow, the larger more terminal ones usually sterile and 
adorning the plant for some time; the more axial numerous, basal 
ones usually fertile, smaller, more or less hidden, and born on short 
peduncles which elongate after fertilization. Calyx forming a long 
stalk-like tube with one narrow lobe as a lower lip, the upper broad 
and four-toothed. Corolla with a large yellow, orange-striped 
standard, two small wings, and a tiny, incurved, beaked keel. Sta- 
mens ten, monadelphous, versatile; five often with fertile anthers 
attached near their base; the alternate ones absent or short and 
fixed at their center. P/J-//7 monocarpous; style long, slender; ovary 
small, at base of the long calyx tube, one celled with one to six ovules; 
after fertilization the floral envelopes drop away, and the ovary, 
now sharp-pointed and strengthened, is pushed by the rigid, recurv- 



312 WALDRON— THE PEANUT 

ing pedicel one to three inches into the soil; after penetration it 
begins to swell and ripen into a fruit. 

Fruit — an indehiscent legume, oblong, reticulated, thick, coria- 
ceous, beaked, swollen around the contained seeds, provided with 
absorptive hairs when nearing maturity. Fruit stem or gynophore 
reddish and slightly hairy above the soil — white and matted with 
absorbing hairs below. 

Seeds — i-i yi cm. long; cotyledons thick, fleshy, oily; radicle 
short, straight. Testa thin, papery, membranous, varying from 
cream to pink to dark red color. 

Sub-species — -Jastigiata Waldron 

Main stem erect and branches all in an upward diagonal position, 
giving the plant a bushy appearance. Fertile flowers axially group- 
ed near baseof plant. Fruit clustered below the main stem. Seeds 
usually small and oblong. 

Variety — White Spanish 

Plant 20-30 cm. tall in average soils — foliage abundant and heavy. 
Pods small, adhering well to the plant, entirely filled by two seeds 
with pink to brownish testa. Very productive with high oil content. 

Variety — Red Spanish 

Similar to the White Spanish, except that the seed coats are red 
and the pods somewhat larger — less productive than the White 
Spanish. 

Variety — Valencia 

Plant 25-50 cm. tall. Pods long, medium thickness, clinging 
poorly to the plant, and containing two to four closely crowded 
seeds with red testas. 

Variety — Tennessee Red 

Plants similar to those of the Spanish varieties. Pods long, cling- 
ing to the plants and containing two to six seeds with dull red seed 
coats. 

Sub-species — procumbens Waldron 

Loosely branching, spreading plants (semi-erect in one variety); 
the stems often later ascending. Flowers and fruit considerably 
scattered along the prostrate stems. Seeds large, more or less 
pointed. 



WALDRON— THE PEANUT 313 

Variety — North Carolina, Florida Runner, African, Wilmington, etc. 

Rank growing plants with dark green massive foliage. Pods not 
clinging well, medium sized, containing two, sometimes three, mod- 
erate-sized seeds with reddish testas. 

Variety — Virginia Runner 

Similar to the North Carolina, but with much larger pods and 
seeds. 

Variety — Virginia Bunch 

Plants semi-erect with light foliage, often appearing among plants 
in fields of the Runner type. Pods large, adhering well to the plant, 
bright, clean, with two, sometimes three, seeds covered by light 
brown coats. 

Variety — Ju m bo 

The same as, or possibly sometimes a strain of, the Virginia Run- 
ner or Virginia Bunch varieties. 

Histology 

Root 

The internal structure of the root of Arachis is of the normal di- 
cotyledonous type. The epidermal relation, however, of young roots 
and the production of root hairs is quite striking. It has been re- 
ported by Pettit and Richter^^ that no hairs are produced on the 
plant. The author, however, found them on all plants examined 
but usually in different position from the normally produced tip 
hairs. Although the tip hairs were found, they were rare and appear- 
ed only on'young vigorous plants. Usually they are present in the 
form of rosettes on and at the base of newly formed side roots. As 
seen in Plate LXXIX, Fig. 4, those produced nearest the base are 
comparatively long, but are gradually reduced in length until none 
appear^ Aside from the position relation, these rosette hairs are of 
the normal root-tip hair structure. The tip hairs when present are 
usually rather short and scattered, occurring on young delicate, usu- 
ally few-branched, roots. No hairs of either type have been ob- 
served on the main root either during germination or later. 

Young elongating roots of the plant which bear no root hairs often 
have their cuticle mucilaginized causing the soil particles to adhere 
as if hairs are present. These roots are often very white, delicate 



314 WALDRON— THE PEANUT 

and semi-transparent. Placing a portion of one on a slide for exam- 
ination under the microscope must be done with care, for the epider- 
mal and outer cortex cells seem readily to fall apart like so many 
poorly cemented bricks becoming loosened. This is due, in part at 
least, to pressure from within, since, as noted by Pettit, the inner 
meristems develop much faster than the dermatogen. This is mark- 
edly evident on the primary root where the surface cells are continu- 
ally peeling off in rows or patches. Sufficient protection, according 
to Pettit, is afforded by a cutinized outer wall being formed by the 
cells which become exposed. Pettit also states that the lateral 
roots act in a similar way, but the present writer did not find this to 
be the case with his plants. These roots are always normal in this 
regard, although very delicate. As they increase in age, their outer 
surface is supplied with a regular periderm, and it is only in the 
early stages of radicle growth that this peculiar habit is observed. 

Ste?n 

The stem is normal for dicotyledons. The epidermis is composed 
of a layer of small, thickly cuticularized cells interrupted by stomata 
in young stems and by a corky lenticel proliferation in old ones. 
Three-celled hairs are scattered along young stems. These are 
typical of many other Leguninosae, each hair having a long pointed 
terminal cell with two tiny, flattened basal cells. There are also 
small crystal cells arranged in groups of two to four, each containing 
one rectangular crystal. The cortex is six to eight layered and com- 
posed of much larger thin walled cells. At the outer extremity of 
the primary bundle areas of the vascular system are large patches 
of highly indurated hard bast. This, along with the quite extensive 
and considerably indurated xylem, give a tough and flexible char- 
acter to the stem. The pith in young stems is composed of round 
extremely thin walled cells filled with starch. As the stem matures, 
however, the pith becomes more or less broken down resulting in a 
semi-hollow condition. Concerning the cambium, a very interesting 
relation is noted later as to its development in the fruit stalk (see 
page 314). 

Leaf 

The leaf structure of the peanut is most striking, especially when 
the xerophytic tendencies of the plant are considered. There are 
numerous average-sized stomata on both surfaces that are neither 



WALDRON— THE PEANUT 315 

raised nor sunken. They average from fifteen to twenty per square 
millimeter, and each is surrounded by two unequal subsidiary cells. 
Both epidermal layers are also supplied with numerous specially 
formed crystal cells (Plate LXXIX, Fig. 5.) which, when the leaf is 
young, are small, each containing a single rounded crystal. Later, 
these cells become fused into what might be called an "epidermal 
vessel," irregular in shape and containing two to thirty crystals 
arranged in clusters or irregular rows. Solereder^^ notes the pres- 
ence of these, bvit does not mention the later fusion into one. In 
attempting to determine the origin of these, a stem apex with a 
young bud attached was sectioned. It was found that in very 
young leaves all the epidermal cells were alike, and devoid of crystals. 
Immediately after the last cell division, however, some of the cells 
increased in size to form the normal epidermis, while others remained 
small to become the crystal-containing cells. In some of these it 
was noted that the small crystal seemed to be a part of the nucleus, 
possibly formed within and by it. It was in a pellicle-like projection 
which later separated away. In all such young cells the crystal was 
imbedded in a protoplasmic matrix which gradually became mucil- 
aginized in old cells. The mesophyll of the leaf is composed of a 
two- to five-layered palisade tissue immediately below the upper 
epidermis and a single layer of water storage cells next to the lower. 
These two features are more typical of a xerophytic plant than is 
the presence of the above mentioned stomata. A loose, comparative- 
ly thin layer of spongy mesophyll separates the palisade and water 
storage layers. The petiole and lower epidermis of the leaflets bear 
the typical three celled hairs already mentioned as found on the stem. 

Fruit 

The anatomy and physiology of the fruit were carefully studied 
for the purpose of discovering, if possible, some facts concerning its 
hypogeal development. Among other members of the Leguminosae 
to share this peculiarity are Amphicarpa monoica, Trifolium subter- 
raneum, species of Voandzeia and of the new African genus Ker- 
stingiella. Amphicarpa bears two kinds of flowers, and accordingly 
two forms of fruit, only one of which develops underground. The 
flower which gives rise to this subterrenean fruit is formed and al- 
ways remains underground. Trifolium subterraneum bears but one 
type of flower formed in heads. The peduncle, after flowering, 



316 WALDRON— THE PEANUT 

lengthens and sinks into the soil carrying the head with it. The 
seeds do ripen above ground, however, and will germinate. 

Differing from both of these, Arachis and the other two genera 
mentioned above have a nearly uniform type of flower, the ovary of 
which is pushed into the ground by a growth at its base. The elong- 
ating fruit stalk is called a "gynophore." 

Anatomy of the Young Gynophore. Observations by the writer 
correspond to most of those of Pettit, whose article is chiefly concerned 
with the structure and development of this organ. Sections made 
longitudinally through young flower buds reveal a nearly sessile 
ovary usually containing two parietal ovules each, on a short funi- 
culus (Plate LXXIX, Fig. 8). There are ii to 13 bundles which ex- 
tend through the base of the ovary to the tip, branching more or less 
in their course. Along the inner edge of each bundle are tannin 
pockets. After the egg is formed and fertilized, the reduced ovarian 
axis begins to elongate to form the gynophore. The ovary and em- 
bryo sac remain unchanged in this condition until the gynophore is 
mature. This will be further discussed under physiology. The 
later cytological study of the embryo was not attempted. 

The meristematic tissue which gives rise to this growth is mostly 
situated just below, and around the base of the ovary. That below 
the ovary forms the pith, while that around the base forms the bundle 
tissue and outer cortex. A few dividing cells forming the latter 
were found well up around the ovarian cavity. The epidermis of 
the tip becomes sharp pointed and highly lignified in its outer walls. 
In Plate LXXIX, Fig. 9, is seen the area at one side of the tip where 
the style was formerly attached. This style is terminal in very young 
buds, but the later lateral position of the scar is prearranged for 
by a special development of a few large lignified epidermal cells at 
one side of its base. (Plate LXXIX, Fig. 8). These grow forward 
a little, and form the sharp point of the ovary. 

Anatomy of the Mature Gynophore. While the structure of this 
fruit stalk corresponds to that of the stem of any herbaceous dicoty- 
ledon, its manner of development resembles that of ordinary roots. 
There are no lateral appendages, and so no nodes and internodes. 
There are two distinct divisions of this organ (i) the epigeal part, 
with smooth, red pigmented surface bearing a few three celled hairs 
similar to those on other parts of the plant; (2) the hypogeal white 
part, whose surface produces single-celled absorptive hairs. (Plate 
LXXIX, Fig. 7.) The surface of the aerial portion is covered with 



WALDRON— THE PEANUT 317 

stomata and lenticels. The epidermal layer of this has a few scat- 
tered crystal cells similar to those found on the stem. 

The cortex is composed of six to eight layers of round thm walled 
cells Internal to this is the vascular system composed of a rmg of 
bundles, each with a large patch of highly lignified bast on its outer 

^' Concerning the cambium layer, Pettit says, "There is an indication 
of the formation of a cambium ring, although it never occurs even 
in the oldest portion of the organ." She goes on to explam the ap- 
parent presence of meristematic tissue between the bundles, which 
the writer considers interfascicular cambium. She continues, "The 
cells are, in their early stages, no larger than the pith cells, but as 
they become older they increase rapidly in both tangential and radial 
diameters. This process, however, appears insufficient to keep pace 
with the growing intrafascicular cambium, and they now become 
meristematic, forming new walls which are at first tangential; later 
radial walls are found. In this manner arise clusters or bands of 
relatively small cells extending from bundle to bundle. While 
these small cells appear like the ordinary meristematic tissue of 
stems whose cambium is formed after the bundles appear, they do 
not continue meristematic; at least in the organs studied there is 
little evidence that these small cells produce lasting tissue of any 
kind, and none whatever of the formation of phloem and xylem ele- 
ments." The above description is correct for the cause and manner 
in which they develop and appear, but the writer feels that this 
tissue is in all respects meristematic as a part of a continuous cam- 
bium ring. The author has seen xylem and phloem elements cut 
off from it to form secondary bundles, and thus proving that it has 
the ability to form these. Also, the presence of such cells in a nearly 
continuous line with the intrafascicular cambium suggests an hered- 
itary tendency to form it even though it is less active than in other 
stems It does apparently connect the xylem patches, but so does 
the corresponding tissue of many stems. The fact that they divide 
even once is sufficient proof, since the resulting cells are permanent. 
The pith is composed of thin walled cells stored with starch until 
the fruit begins to form. Later the pith, breaks down as does that 
of the stem and the gynophore becomes more or less hollow. 

The anatomy of the subterranean part of the gynophore differs 
from that above ground in the following ways: (i) All of the epi- 
dermal cells become extended outward into long absorptive hairs 



318 WALDRON— THE PEANUT 

simulating typical root hairs. (2) a growth in thickness occurs by 
a process similar to that of periderm formation, by which the diam- 
eter of the subterranean part is somewhat increased. Pettit notes 
another difference in the absence of what she calls plasmolytic cells 
situated in the center of the cortex of the epigeal part. These cells 
have not been observed by the author. 

The absorptive hairs (Plate LXXIX, Fig. 7) are large, unbranched, 
one celled and average nearly a millimeter in length. Each is 
slightly enlarged at the base which represents the size of the original 
cell from which it springs. No stomata were seen, but lenticels 
were present which developed into a white proliferation of cells 
when exposed to a moist atmosphere as did some of those of the 
epigeal portion. 

The examination of a cross section of this hypogeal area showed 
the outer layer of the cortex dividing into two to four layers of cork- 
like cells. The cells of this sub-epidermal layer are somewhat larger 
than those of the rest of the cortex. Although these apparent phel- 
logen derived cells have tbe appearance of periderm, according to 
Pettit, they are free from suberin, as would be expected from the 
presence of absorption hairs on their exterior. 

Anatofny of the Young Fruit. As noted above (see page 316) the 
ovary, situated at the tip of the gynophore remains inactive until 
the time comes for fruit maturation. The epidermis at this time 
is composed of much deeper and narrower cells radially, than that 
of the non-hairy part of the gynophore. They become deep, tap- 
ering and lignified at the tip forming a hard, but not capped apex. 
The lumen of those at the tip contain numerous granules that are 
not evident further back and suggest a relation to the geotropic 
reaction of the gynophore. Three or four hypodermal layers, that 
later form the outer mesocarp, are composed of markedly cylindric 
cells. A branching bundle system within this is a continuation of 
that of the gynophore which gradually disappears toward the tip. 
Just interior to this are a few layers which later assume marked 
appearance and importance as tissue which becomes gradually lig- 
nified to form the strengthening inner shell layer of the fruit. The 
innermost tissue next to the ovarian cavity is composed of several 
layers of tiny nearly square cells arranged in radiating rows. 

Anatomy of the Developing Fruit. When the ovary begins to en- 
large, the epidermal cells elongate longitudinally and later become 
ruptured. This epidermis with the subjacent layer, is rubbed or 



WALDRON— THE PEANUT 319 

Stripped off, which is a very unique event in fruit maturation. Ap- 
parently the epidermis does not keep up with the growth from within. 
Within the epidermis several layers of periderm have already ap- 
peared, similar to, and continuous with, that of the lower end of the 
fruit stalk (gynophore). Till this occurs and until the fruit is one 
half to three quarters full size, no hairs are formed on any part of 
the ovary or young fruit. About this time, however, and lastmg 
until the fruit is mature, there appear on this layer irregular, often 
branched, one-celled absorptive hairs (Plate LXXIX, Fig. 6). 

The developing bundles have increased in size, and with their 
connecting branches, form ridges which later give the reticulations 
to the fruit. Meantime a few layers, just interior to these, are be- 
coming remarkably indurated to constitute the solid enclosing 
chamber of the mature fruit. The inner endocarp area of small 
cells has enormously thickened and from the time the fruit has be- 
gun to swell until nearly ripe, this area is composed of very large, 
thin walled, pith-like cells which contain sugar. This area remains 
thick and the developing seed small until a short time before maturity. 
It forms a large part of the fruit at this time. 

Anatomy of the Mature Fruit. Winton notes the presence of an 
epidermis and states that it is not easily seen. As noted in the dis- 
cussion of the developing fruit, this could only be a pseudo-epidermis 
that he has mistaken for the already shed epidermis, and the fact 
that it is the small-celled third layer of the ovarian tissue may ex- 
plain why it is distinguished with difficulty. As in the nearly ma- 
ture fruit, absorbing hairs are present as wall extensions of it. These 
hairs were not observed to be as often branched as in the younger 
fruit. One or two appeared to be septate. 

Just below the outer absorbing layer are several rows of brick 
shaped, thin walled cells, simulating those of the hypogeal gynophore 
in appearance and position. Within this are several layers of thin 
walled cells that have collapsed. Apparently new cells were not 
produced for this area to allow for the expansion of the fruit. These 
surrounded a few layers of unbroken, rounded cells in which are em- 
bedded the branching vascular bundles. Large bundles are arranged 
longitudinally, and are connected by short smaller cross bundles, 
the whole system forming the reticulation of the peanut shell. The 
xylem and phloem of these have become highly lignified. 

Attached to the inner edge of the bundle network is the solid hard 
enclosing shell of the peanut, composed of the now mature lignified 



320 WALDRON— THE PEANUT 

mass of cells mentioned in connection with the maturing fruit. The 
cells forming this are now remarkable in their shape, size, wall thick- 
enings, and branches. (See Winton's article.) 

The structural relation of the carpellary wall to that of a leaf, 
from which it is modified, is recognized, but with more difficulty 
than that of many aerial leguminous fruits. By carefully splitting 
open a fruit, as one ordinarily shells a peanut, it will be noted that 
the seeds are attached to the somewhat convex side opposite that of 
the beak. Thus the dorsal is recognized from the ventral suture. 
Histologically these areas are not discernable in young ovaries, 
except by noting the location of the ovule attachment, or that of 
the style. This also locates exactly the position of the beak in 
the mature fruit. In mature fruit shells there is a ventral suture 
along which they quite readily split, due to a weaker, less lignified, 
loose line of tissue as seen under the microscope. 

Concerning the exocarp, mesocarp and endocarp and their origin, 
there is such a marked change and fusion of parts that any sharp 
line of demarcation is impossible. The exocarp, which is typi- 
cally derived from the lower leaf epidermis, is lost during fruit ma- 
turation. The name endocarp, derived from the lower epidermis, 
might be applied to the soft, internal tissue called inner parenchyma 
by Winton. Practically the whole of the shell then would be the 
mesocarp and can be subdivided into hypoderm, bundle area and 
bre layer. 

The anatomy and cytology of the embryo not having been at- 
tempted, that of the mature seed is also omitted. For details oj 
the latter the reader is referred to Winton's article. 

Physiology 

Root Hairs 

To the writer, the thought suggested by others, as noted in the 
histological discussion, that Arachis bore no root hairs, seemed con- 
trary to expectation. *The plant, with a semi-xerophytic tendency, 
and growing well in a warm, loose soil, would be expected to have 
them, at least when moisture is sufficient to stimulate their produc- 
tion. 

Plants started in the greenhouse and carried on in flower pots 
were therefore examined. Of twenty-five plants, one showed hairs 
present near the tips of two of the young vigorous growing roots. 



WALDRON— THE PEANUT 321 

They were, however, very short and comparatively few in number. 
It was noted, however, with some surprise, that on the roots of 
nearly every plant, tufts or whorls of hairs were present as rosettes 
at the base of some of the side rootlets. These were much longer 
than the first-mentioned type, as is set forth in the figure. The 
possibility that the influence of potting may" have in some way 
caused the development of these rosettes as well as tip hairs, led to 
an examination of the roots in the center of pots, and of roots on 
plants which had been carried forward in boxes (2x3x1^^ ft.) 
Such roots have less air drainage than those along the inside wall 
of a flower pot. Plants were removed, their roots carefully washed 
out, and tufts of hairs were found at the base of many newly formed* 
side roots. 

The presence of normally produced tip hairs was carefully watched 
for, but none was found. The only plant mentioned which had these 
was one, the roots of which were in a moist air compartment, formed 
by the drainage hole of the bottom of the flower pot, the broken 
crocks just above, and the cinder bench below. This suggests, 
therefore, that optimum oxygenation is a necessary factor for the 
tip hair growth. None were found on the roots of any plants in the 
soil, either under dry or moist conditions. Since the plant seemed 
to have at least a hereditary tendency under certain conditions 
to produce these normal tip hairs it was considered worth while to 
determine, if possible, the exact causes or stimuli which afi^ect their 
growth and that of the rosette type. Observations and experi- 
ments were, therefore, carried on with this in view, as well as to 
determine the causes and method of production of, and differences 
between, the two forms. The results of this investigation are de- 
scribed in succession to the following discussion of the works of 
others on this subject. 

Concerning the presence and absence of root hairs, Strasburger^^ 
states that in some few instances as in some conifers plants bear no 
root hairs. Jost"' says that few plants produce none, probably re- 
ferring to aquatic types. Haberlandt" refers to two stages in the 
specialization of absorptive tissue in plants, (i) Some plants are 
content to increase their absorptive surface by a greater output of 
side roots, the epidermal cells of which are flat or slightly convex in 
their outer walls. But he states that this type includes marsh and 
aquatic plants, and is less advanced in this regard. If this is a stage 
in specialization, would it not be possible to think of it as a reduc- 



322 WALDRON— THE PEANUT 

tion change following a former evolved condition in root hair pro- 
duction due to adaptation to changed environment? Corn and 
many other plants produce none when put in water. (2) Other 
plants produce root hairs near the tips of their roots by elongation 
of the outer epidermal cell walls. Since many hair producing plants 
cease to bear these when in contact with water or saturated soil, 
it would seem to the writer that instead of being two stages of spe- 
cialization, it is an example of two types of absorptive tissue depen- 
dent on ecological factors. It is a more or less epidermal surface 
extension for absorption, dependent upon the amount of causing 
stimuli present. The hairless aquatic plants may have had hairs 
at some time, and some do produce them when growing in dry soil 
again. 

As to the cause for root hair production, Pfeffer^^ states that 
too little or too much water hinders, while darkness and contact 
accelerate. Snow in an extensive investigation on the causes of 
their development finds that they are accelerated by a retardation 
of growth, by mechanical means, or substratum resistance, espe- 
cially if the roots of such are allowed to grow in a moist atmosphere. 
She finds that they are retarded by a saturated atmosphere at high 
temperatures, by a lack of oxygen, and by a saturated soil; light and 
darkness, however, have no material effect. 

Observations and Experiments with Root Hairs 

It was noted that if seeds were planted in a heavy soil and germ- 
ination was retarded by lack of moisture, the hypocotyl would some- 
times swell considerably and give off adventitious roots which 
branched profusely. By drawing the soil away, after the radicle 
had grown an inch or two, until the lower end of the hypocotyl was 
well exposed, the upper part of the side, and of the adventitious 
roots with their hairs could b% kept growing in saturated air. This 
gave a good opportunity to determine the effect of sunlight on the 
growth of hairs, as compared with those on a few plants whose roots 
were kept in the dark, but also exposed to the air. The foliage of 
both sets of plants had the same leaf exposure, so that the activity 
and growth were -as near the same in all as possible. In all cases, 
both in light and in darkness, the rosette hairs were found at the base 
of the side rootlets and there was no marked difference in their size 
or abundance. This corresponds to the results of Snow, except 
that in her observations she noted a slightly longer growth in the 



WALDRON— THE PEANUT 323 

dark. This was possibly due to a greater drying out in light in 
her experiments. No normally produced tip hairs were observed. 

Temperature. Plants with roots exposed were kept at 90° F. 
to 100° F. in a moist chamber. Others were kept at 60° F. to 70° F., 
the other conditions being the same. Rosette hairs appeared on 
all the plants, but at the higher temperature they were much more 
luxuriant and abundant. Tip hairs were found near the tips of 
several roots on two of the plants growing at the high temperature. 
These two plants producing both types of hairs were the most vig- 
orous of the set of twenty in the experiment. These results do not 
correspond with those of Snow, where a high temperature and hu- 
midity retarded their growth. This can possibly be explained by 
the fact that the peanut requires a higher temperature for optimum 
growth than those plants with which she experimented. 

Soil. Plants in loose sandy soil composed of one-half light loam 
and one-half sand grew vigorously. After germination they pro- 
duced numerous long and almost pure white roots, a few of which, 
after reaching the side of the pot or box, bore a limited number of 
tip hairs. No rosette hairs appeared until the plants were one to 
two weeks old and quite well established. Tip hairs appeared on 
one plant only, of those that were older than three weeks. Plants 
in light loam, without any mixture of sand, grew slowly and the 
rosette hairs were the first and only type observed, after the side 
roots had developed. They appeared on all the plants examined 
after from one to two weeks' growth. Tip hairs were observed on 
a two months' old plant which had been retarded in its growth, 
and, when repotted, a few delicate roots appeared which bore a 
very few scattered tip hairs.* Rosette hairs could be found on any 
plant of any age, except the young vigorous specimens of less than 
two or three weeks' growth. 

On seedlings of various ages no hairs of either sort were ever ob- 
served on the primary root. Many seeds germinated in sandy soil, 
and on sterilized wet cotton in test tubes, did not produce them even 
under optimum conditions of heat, air and moisture. With sufficient 
moisture, however, rosettes always appeared on the bases of the 
side roots. Those in test tubes grew slowly because of lack of 



*0f about fifteen such plants examined this one was the only one in which 
they were observed. 



324 WALDRON— THE PEANUT 

water, and as a result rosette hairs were the only type observed. 
These were absent on the roots furthest from the moist cotton. 

Concerning the function of root hairs on the radicles of seedlings, 
Haberlandt and others state that one reason for their early forma- 
tion on these, is, that the main root may have sufficient anchorage 
in order to rapidly penetrate the soil for its immediate needs. Evi- 
dence presented by the peanut thus entirely contradicts such a 
view, indicating that they are not necessary for this purpose. Such 
seeds as those of the peanut can alone supply adequate food material 
for germination if water is present. The radicle elongates and pene- 
trates a light soil with great rapidity without them. This may be 
one reason why a light sandy soil is best for this species. This 
thought also suggests an interesting relation to the hypogeal fruit 
production. The plant always maturing its seed under ground 
would not need such anchorage for its first root growth, 
even though it were a desirable feature. The fruit wall acts also 
as an aid. The writer feels, however, that the reason why hairs 
are not present here is that the outer layers, in stripping off (see 
page 314), do not allow their development. The fact that side 
roots, which do not show this peeling, will form them under proper 
stimuli is evidence of this. Even these do not often produce them, 
probably because of their very loose structure (see page 314). The 
cells which are best adapted to respond are at the base of side roots, 
thus rosettes are formed. 

To summarize these observations, the results of the root hair 
experiments on the peanut indicate that (i) light and darkness have 
no effect on their production; (2) high temperature, with sufficient 
moisture and air, accelerate the growth and production of the rosette 
type; (3) loose sandy soil, with root aeration, stimulates hair growth 
on the tips of young plants, and possibly also on old plants, if a 
period of retardation is followed by a suddenly renewed root vigor. 
The rosettes of hairs may appear on any plant of more than one to 
two weeks' growth. The tip hairs are found only on young roots 
that are undergoing a vigorous elongation in a natural or artificial 
moist air space at a high temperature. Low temperature, lack of 
oxygen and wet heavy soil prevent the normal tip type from appear- 
ing and retard the rosette form. None appear on the radicle. The 
cause for the production of the rosette hairs at and on the base of 
the side roots is hard to explain. It may be that, at the time the 
side root is penetrating the cortex and epidermis of the main root. 



WALDRON— THE PEANUT 325 

the root tip tissue here is more active and vitalized than later, and 
so is more sensitive to external stimuli. It was noted that when tip 
hairs were produced usually no rosettes were present. Possibly 
these offset the need for tip hairs, or at least utilize energy which is 
lacking for their later formation. 

Absorption 

From the foregong observations on the roots and root hairs of 
the peanut, it is evident that the young plant absorbs its water and 
mineral foods by any one, two, or all of the following means, depend- 
ing on environment and growth conditions: (i) Through the epi- 
dermis of young roots the thin cuticle of which is mucilaginized; (2) 
By means of normal tip hairs on vigorous growing roots; (3) By 
means of the rosetted, basal hairs. The first and last are undoubtedly 
the most important of these. As soon as the fruit stalks appear and 
reach the soil, hairs are at once formed from the epidermal cells of 
these. The older plants then have a much more extensive absorbing 
surface from the formation of a considerable number of gynophores. 

Proof that these hairs do supply water to the plant is indicated 
by the fact that, according to Pettit, when the roots of such are 
severed the plant continues active and apparently uninjured for 
some time. The xylem of the gynophore bundles, although not very 
large, is sufficient to carry a considerable quantity of material. The 
nearly mature fruit must also absorb some water as indicated by 
the presence of delicate absorbing hairs. How important this is it 
is difficult to say. That they are not absolutely essential is evident 
from the fact that the fruit continues to swell somewhat if trans- 
ferred from the soil to the air, causing the hairs to dry up. The 
absorbing fruit stalk undoubtedly takes the place of roots to a cer- 
tain extent. Root tubercles, which also appear at about the same 
time, should be noted too in this relation, since some other nodule- 
producing members of the Leguminosae, as is well known, seem to 
have a reduction of root hairs. The absorbing surface of roots alone 
on these older plants is comparatively small. 

Development 

Germination. The writer, in attempting to raise plants for study 
in the greenhouse, had some difficulty in keeping insects and mice 
away. Some of these seemed to have no difficulty in locating the 
seed even before germination. A wire cage was finally built which 



326 WALDRON— THE PEANUT 

controlled these pests. Further trouble was experienced, however, 
unless great care was used in planting and watering. It was found 
that unless they were brought forward in loose material like sphag- 
num or well aerated sandy soil, they rotted in one to two days. If 
pure sand were used, they would rot if kept even moderately wet. 
The method finally used which succeeded was to plant several to- 
gether, allowing a considerable degree of aeration. When these 
produced an inch or two of radicle, they were separated and trans- 
ferred to individual pots with the cotyledons half exposed. Seeds 
planted in the shell succeeded well, as this seemed to allow also for 
free aeration. The ease with which the seeds rot is likely due to its 
weak protection by the testa. This thin papery coat is easily rup- 
tured and the embryo, rich in food material, seems to be very sus- 
ceptible to infection by molds and decay-bacteria. If growth is 
rapid, however, the increased oxidation gives it vitality to resist. 
Those who raise peanuts say that good drainage in a loose soil is 
absolutely essential for success. The plant must start quickly and 
be kept growing. If planted in the uninjured shell, which is sterile 
within, there is less likelihood of infection before it gets well under 
way. A comparison was made by Bennett^^ of growing peanuts 
from shelled nuts, nuts broken into two parts, dry and unshelled 
nuts, and unshelled nuts which had been soaked in water for 12 
hours and buried in the earth below the frost line for different per- 
iods. The most perfect stand was obtained from nuts planted in 
broken pods. The results seemed to indicate that when nuts had 
been thoroughly wet and moist for a short time they would produce 
a good stand, and save the expense of shelling. This corroborates 
the author's thought that the seed benefits by free oxygen and pro- 
tection furnished by the shell in order to start its growth success- 
fully, at least in anything but an extremely loose soil. 

Later Growth. After the radicle has reached two or three inches 
the cotyledons are pushed about 1 cm. into the air by the elongat- 
ing hypocotyl. The hypocotyl often becomes thick and fleshy in 
its cortex. This is more marked when growth is retarded from some 
cause, and then the lower end becomes tuberous from a deposition 
of sugar. The roots of such are not able to utilize the food as fast 
as it is supplied from the seed. When the soil is light and the tem- 
perature optimum, the formation of an extensive root system re- 
sults (see page 323). Under these conditions while the food of the 
cotyledons is still available, the plant grows rapidly for about 



WALDRON— THE PEANUT 327 

two weeks, followed by a period of very moderate development. 
Audouard^® states that the plant grows slowly during the first half 
of its existence, and that the most rapid growth takes place after 
about ten weeks. This indicates a relation to the formation of the 
gynophore and root tubercles again, both of which appear later. 
This makes possible a greater activity in growth of the plant. One 
feature somewhat difficult to understand is the presence of the num- 
erous stomata on both ^idermal layers. How is the water balance 
. kept with such a reduced hair surface, especially on the roots of 
plants not yet producing fruit? 

If the seed is deep, the hypocotyl elongates accordingly. If the 
seed is planted in the shell, it will push up through three or four 
inches of soil. It is often much curved and twisted in its efforts 
to extricate the cotyledons from the shell. These remain green for 
two or three weeks, when they wither and drop. Concerning the 
presence of food materials during growth Audouard states (i) that 
there is sugar in all parts of the plant, which decreases in amount 
during fruit maturation; (2) That starch in the root and stem in- 
creases from the beginning to the end of vegetation; (3) that fats 
increase for six to nine weeks, that is, until the fruiting period, when 
they suddenly decrease in the vegetative organs; (4) that proteins 
decrease in roots and stems at flowering time and increase in the 
fruit. The writer has observed that the gynophore is well stored 
with starch until the ovary begins to grow, when apparently much of 
it is carried as sugar to the inner fruit tissue, forming there the 
broad, delicate-walled sugary endocarp (see page 319), — thus the 
reason why immature fruits are sweeter. Some of this sugar at 
least is apparently gradually transferred to the testa and there 
stored temporarily as starch. Later, both this and that from other 
sources (gynophore and stem) are transferred to the cotyledons and 
largely stored as oil. Since the carbohydrates are early furnished 
and carried to the gynophore and stem, the thought arises as to the 
possibility of the fruit maturation being largely independent of the 
roots of the plant. The other food materials can be obtained from 
the soil by the fruit, and proteins can be formed in darkness, so there 
is no known reason why this should not occur. 

Biological Considerations Concerning the Fruit and Gynophore. 

Observations on the Gynophore. In his work on "The Movements 
of Plants,'" Darwin"^ says that while apheliotropism may act in 



328 WALDRON— THE PEANUT 

some slight measure on the downward growth of this organ,geotrop- 
ism is unquestionably the exciting cause. The writer proved this 
by inverting two plants which had produced several gynophores 
whose tips were about to pierce the soil. As seen in Fig. 1 1 the 
tips' turned away and became reversed in position. This not only 
proved the effect of gravity, but also that the hydrotropic reaction 
of the organ was weak or lacking. They acted in a similar way even 
if the soil was saturated. When tips were allowed to penetrate 
wet sphagnum, and then the plants reversed, they would recurve 
downward and grow out of it. When the plants were righted again 
the tips also turned back thus forming an S curve (Plate LXXX, Figs. 
II and 12). The presence of definite granules in the lumen of each 
of the epidermal cells of the gynophore (see page 318) at the tip, and 
their absence anywhere else, suggests the possibility of such being 
the structures by which this organ perceives when it is out of line 
with gravity. This has been discussed by others in connection with 
the presence of starch grains in root tips. The writer found that 
by cutting off the tip of the gynophore, growth continued, but there 
was no reaction to gravity when the plant was inverted. The ap- 
parent homology between the behavior of the root apex and of the 
gynophore apex is highly suggestive. 

Darwin refers to the means by which this organ penetrates through 
the soil. He says, "the sharp smooth point of the gynophore en- 
ables it to penetrate the ground by mere force of growth, but its 
action is aided by a circumnutating movement." The anatomy of the 
organ is also suggestive. The patches of hard bast give strength, 
while their separation, even though in a close ring, gives pliability. 
Pettit states that the hairs produced at the tip are also an aid in 
holding it firmly. Although this happens to be of some assistance, 
the writer would question to what extent, since the relation of the 
radicle to soil penetration puts a new light on this matter. Hair 
experiments, similar to those of Pettit, were made with plants bear- 
ing young gynophores, which had not yet reached the soil. Pettit 
found that by putting these in a moist chamber a narrow zone, 
averaging 3 mm. in length, always appears one to eight millimeters 
from the tip. The writer found by repeated experiments that this 
zone might be as much as 5 cm in length (Plate LXXX, Fig. 13). 

In discussing these in relation to those of roots, Pettit says: "In 
comparing the growth of gynophore hairs with that of root hairs it 
must be remembered that the growing point of the gynophore cor- 



WALDRON— THE PEANUT 329 

responding to the punctum vegetationis of the root lies just below 
the ovary which occupies the extreme tip of this organ. The ovary, 
however, is almost microscopically small and remains so during the 
growth of the gynophore. To illustrate the extremely small space 
occupied by it, the hairs which were not more than one millimeter 
from the tips of the gynophores as mentioned above were still below 
the growing point under the ovary. While this difference in the 
position of the growing point exists between root and gynophore, 
the difference which it makes in estimating the relative distances of 
the hairs from the tips is practically nothing. 

"The resemblance between these hairs and those of roots was fur- 
ther tested by repeated experiments in pulling young gynophores 
carefully from the soil. The minute portions of earth clung to the 
hairs and refused to be separated from them in the same manner as 
in the case of root hairs. In several instances these hairs were tested 
for acids and were found to respond readily to the litmus paper test. 

"Still another experiment was made which furnishes strong evi- 
dence that one function of the gynophore hairs corresponds to the 
chief function of those of the root. A large, well developed, thriftily 
growing plant was cut in such a manner as to separate the whole 
root system from the stems, but the latter were still connected with 
the ground by numerous well grown gynophores. The result was 
that the plant so treated after two weeks still presented nothing to 
a superficial inspection to distinguish it from others in its vicinity 
whose roots were left intact. Closer examination showed that some 
branches were dead; but the majority were putting out new leaves 
which appeared quite as strong and healthy as any of those on sim- 
ilar plants in the vicinity which were supported by roots. Un- 
fortunately these experiments were begun late in the season, and the 
appearance of the frost prevented their continuance." 

Fruit Maturation. Other writers state that all attempts' to make 
the gynophore produce aerial fruits by digging away the soil as the 
gynophore elongates fail. It is also well known that any such stem 
dries up unless it reaches the soil by the time it is two to three inches 
long. The length to which it grows before drying varies with the 
humidity of the air. Experiments were thus made in an attempt to 
determine what caused the ovary to enlarge, and what would pre- 
vent it. Plants with gynophores of various lengths were put in a 
saturated atmosphere and not allowed to penetrate any substratum. 
In all cases the gynophores continued to elongate and become green 



330 WALDRON— THE PEANUT 

for about a month. They usually attained five or six inches in 
length and then wilted just back of the ovary. The longest gyno- 
phore produced in this way was seven and one half inches in length 
— nearly twice as long as any seen by the writer in the soil. Hairs 
developed which gradually died away until there were but a few near 
the tip. Other gynophores were allowed to grow in test tubes of 
tap water, some kept in the dark, others in the light. These pro- 
duced no hairs. Two of those in darkness, after eight weeks, pro- 
duced a small one seeded fruit. The remainder produced none. 
Others were allowed to grow into sphagnum and pure sand and re- 
sulted in fruit formation in both cases. Gynophores which had pen- 
etrated soil and whose ovary had begun to swell were exposed to a 
saturated atmosphere and to ordinary greenhouse conditions. In 
the former case, the fruit turned green and continued to grow 
slightly, while the latter turned green and remained small. 

The results of these trials, although not at all conclusive as to 
evidence offered, indicate that (i) a thigmotropiCy hydrotropic or ap- 
oheliotropic stimulus, or a combination of these, is necessary for the 
ovary to begin maturation, but (2) that a continuation of such is 
not necessary, since the ovary continues to develop somewhat if 
removed from the soil after its growth has begun. This develop- 
ment, however, is somewhat abnormal. All successful experiments 
were produced in complete or partial darkness, although those 
in the moist dark chambers failed. This suggests the necessity 
of the first two factors, i. e., water and contact. More research is 
necessary in order to clinch this point and determine which of the 
three is the most important. 

From the writer's observations and from the varying results of 
the above attempts at fruit production, he feels that two things 
should be kept in mind — (i) the condition and activity of plant 
growth, (2) the ability of the plant to possibly supply the necessary 
substances to the fruit in two ways — (a) by direct absorption of 
some of them from the soil with the carbohydrate supply from the 
plant; (b) by transfer of all necessary materials from the vegetative 
organs into the fruit. A number of plants that became pot-bound, 
when several gynophores were being formed on them produced only 
one or two small fruits. Similar plants that had abundant pot- 
room produced several. Weak plants may have been experimented 
with. In the field, many poor fruits without seeds called "pops" 
are found — due possibly in part to this same cause. 



WALDRON— THE PEANUT 331 

The chlorophyll formed in the fruits exposed to light was found 
to be exterior to and around the bundles that form the pericarp re- 
ticulations. The testa and cotyledons also became green. This is 
an interesting point since it indicates the retention through long 
millenia of the factors necessary for chlorophyll formation. 

Watt has observed in India that red ants are frequently found 
working harmlessly around growing fruits in the soil. This would 
be of benefit to the fruit since aeration of the surrounding soil would 
allow for greater absorptive hair development. What benefit the 
ants might obtain is hard to tell. 

Fruit Hairs. It should be kept in mind that the fruit hairs are 
different in origin from any found elsewhere on the plant (see page 3 19). 
Points of evidence indicating this are — (i) that the epidermal and 
subjacent layer of cells is seen to be thrown off (see page 319 and Fig. 
6). (2) That the hairs are different from any found elsewhere 
on the plant, all of which are truly epidermal. (3) That this differ- 
ence, that is the bifurcations of the hairs, indicates the irregularity 
of growth of the mesophyll of leaves. (4) That no hairs appear on 
the fruit until it is well grown and the two outer layers have been 
discarded. 

Other queries raised here are: why is the second layer of cells 
discarded as well as the epidermis? and why doesn't the periderm- 
like tissue begin its formation by divisions taking place in this layer, 
as is the case with the hypogeal gynophore, instead of in a deeper 
layer? One possible answer is, that this corresponds to that layer 
of water storage cells next to the lower epidermis of the leaves of 
Arachis. This layer still persists in the carpel, and, being large- 
celled and less able to divide, is thrown off with the epidermis. 

Conclusions Jrom Physiological Studies 

It remains to be considered how far the facts ascertained in this 
study contribute to the knowledge of hypogeal fruit production. 
The fact that the fruit of so many plants of varied families seeks the 
ground must be regarded as significant. Tschirch, in a paper on 
Leguminosae, says that one group of nitrogenous compounds pro- 
duced by the Leguminosae can be formed only in darkness, and sug- 
gests this reason for such a habit. It has also been suggested that 
the fruit is thus protected from animals. 

Concerning the present studies, the following new facts stand 
out quite prominently — (i) The tendency to fruit formation in 



332 WALDRON— THE PEANUT 

moisture and darkness. (2) The formation of periderm-like tissue 
on the hypogeal gynophore and fruit. (3) The formation of hairs 
on the gynophore-epidermis and pseudoepidermis of the fruit. That 
water is absorbed by these hairs is undoubtedly true. The most 
puzzling new structural feature is the second, where thin-walled cells, 
not suberized, are laid down by a late-formed cambium layer. Such 
is rare in leaf tissue. The bud scales of Horse Chestnut and other 
trees produce a limited amount of suberized tissue in this way. Two 
to three layers are always produced on the gynophore when this 
organ is subjected to a saturated atmosphere. This suggests a 
possible water storage tissue, or it may be a result of pressure from 
within when more water is absorbed. Cells are possibly necessarily 
cut off to allow for this expansion. 

Finally, it is suggested that if the plant does not require more 
nourishment from the soil than might be supplied by root hairs, and 
yet forms such hairs on the gynophore and nearly mature fruit, it 
may be more advantageous to take some of its food by this special 
method. Perhaps certain desirable changes are made possible by 
such foods always being in darkness. Is it then darkness, or extra 
water supply that the fruit seeks? Whatever the reason, the re- 
sulting advantage is full maturation and selective survival of the 
seed, which is highly concentrated in its food constituents. 

Uses of the Peanut 

To most people outside the peanut growing sections of the coun- 
try, the peanut suggests only an unessential food article, — a delicacy 
to many, — in the form of the roasted or salted nut, peanut con- 
fectionery or peanut butter. During recent years, however, and 
especially in the past year or two it has become of utmost importance 
as a staple article of diet and otherwise. In the cotton growing 
states it is saving the day for many farmers who have failed with 
cotton growing because of the new insect pests or other reasons. 

Uses as Human Food. The following from Beattie^^ in this con- 
nection is worth quoting: "The use of the peanut for eating from 
the shell is most important and popular, but the quantity of shelled 
peas that are first roasted and salted and sold by the pound is con- 
stantly increasing. Some of the better grades are first shelled, then 
roasted after which the halves are broken apart and the germ re- 
moved giving the meats a blanched appearance rendering them very 
desirable for table use. Great quantities of shelled peas are used 



WALDRON— THE PEANUT 333 

every year in the manufacture of peanut candies and brittle, both 
alone and in combination with other nuts, pop corn or puffed rice." 

During recent years great quantities of shelled peanuts, especially 
of the Spanish variety, have been employed for the manufacture of 
peanut butter. It is used in the preparation of vegetarian meats 
after a portion of the oil has been pressed from the nuts. This 
extra oil and that pressed from nuts grown for the purpose is used 
in thinning peanut butter and is as good for every purpose as is 
that of the olive. It is one of the sweetest vegetable oils. Articles 
fried in it keep well for a longer time than in olive oil and have an 
agreeable odor and flavor. It is mixed with cotton-seed oil to im- 
prove it for salad purposes. 

Peanut meal or flour of finely ground nuts is used in confections, 
cakes and bread making. It is used as a substitute for rice and other 
flours. Watt reports that in India the unripe nuts are sweeter (as 
indicated in the author's discussion on the physiology of the fruit) 
and, being more easily digested, are given women whose milk supply 
is insufficient for their children. These unripe fruits, when fresh, 
make an agreeable boiled dish. The very tender leaves of the plant 
are sometimes cooked with ground coconut. 

Concerning the food value and change of the peanut from the 
category of a luxury to that of a more staple item of diet for man, 
the following is taken from "The Literary Digest" for April 13, 191 8. 
"The peanut enters into the preparation of most of the vegetable 
'meat substitutes' long warmly advocated by the vegetarians and 
now made more conspicuous by the governmental admonition to 
'eat less meat;' and peanut 'butters' or 'pastes' are widely used. To- 
day the value of the peanut crop, which is divided between the pro- 
duction of the promising peanut-oil, peanut-cake for animal fodder 
and roasted peanuts for human food, has begun to total many mil- 
lions of dollars. At the University of Wisconsin, Daniels and Lough- 
lin have demonstrated by feeding-experiments on animals that the 
peanut can supply adequate protein ... in sufficient pro- 
portions for growth and reproduction. It can also furnish an abund- 
ance of the water-soluble vitamin. The food as used in the human 
dietary does not, however, yield the growth-promoting fat-soluble 
vitamin, which has come to be recognized as a remarkable consti- 
tuent of butter fat and egg fat; nor are the inorganic constituents 
adequate in quality to supply sufficient calcium and certain elements. 
Of course, the peanut is not used as a sole source of nutrients for 



334 WALDRON— THE PEANUT 

man; nevertheless, the dehneation of its physiologic value enables 
one to define more intelligently the place which it can take in the 
ration. Daniels and Loughlin foresee an increasing usefulness for 
the peanut, now that its real value has been scientifically established. 
When we consider the broad areas, they say, which may be adapted 
for growing the crop, and the fact that our food supply tends toward 
a wider use of the seeds of plants, it seems appropriate to expect 
that the peanut, when rightly supplemented, will form a staple ar- 
ticle of the human dietary. Like the soy-bean, which has lately 
come into prominence in American homes, the peanut needs only 
to have added suitable inorganic salts and the fat-soluble accessory 
to make it a complete food." 

Uses as Food for Live-Stock. Beattie is quoted in this connection 
as follows: "In the factories where peanuts are cleaned, shelled, 
and graded for the market there is always a certain percentage of 
cleanings and inferior stock that can readily be turned into stock 
foods. The outside shell, or hull, of the peanut, is rich in food ma- 
terials, but is extremely difficult to reduce to a condition in which 
it can be fed. In large cleaning factories the shells are generally 
used as fuel, and the ash resulting therefrom is valuable as a fertil- 
izer, often containing as high as 3 per cent of phosphoric acid, 9 
per cent of potash and 6 per cent of lime. 

"The thin brown covering of the peas has a feeding value almost 
equal to that of wheat bran. These hulls are especially desirable 
for mixing with the smaller particles of broken peas for stock feed- 
ing. In large factories where peanuts are prepared for the manu- 
facture of peanut butter and similar preparations the waste in the 
form of small particles of the meats and the germs is considerable 
and this is sold to farmers for feeding purposes. In some cases the 
waste is mixed with a portion of the hulls and finely ground or chop- 
ped before leaving the factory. Peanut hulls make an excellent 
bedding for use in stables, and by using them in this manner and 
hauling the manure upon the land their full value can be obtained. 
Broken peas and germs are used largely as a food for hogs, but 
both should be fed in moderation and in combination with some 
grain, as the peanut fed by itself will produce a hog having soft fat 
and inferior meat. The famous Smithfield hams and bacon come 
from hogs that are fed partly on peanuts, the practice being to turn 
the hogs into the peanut fields after the crop has been gathered and 
allow them to glean the pods that were lost in harvesting. The 



WALDRON— THE PEANUT 335 

principal objection to the use of peanut by-products as stock feed 
is their tendency to become rancid very quickly. The germs, which 
are high in nitrogen content, become rancid and bitter in a short 
while and should not be kept on hand for a greater period than fifty 
or sixty days." 

Peanut cake is a stock feed composed of the remains of seeds when 
expressed for oil and is extremely rich. As hay, peanut tops are 
worth just as much as alfalfa, pound for pound. Even the entire 
plant is used, and often chopped fine for this purpose. It forms ~ 
a well balanced ration for dairy cows. 

Use as a Soil Renovator. Here again the peanut is rapidly be- 
coming a crop of much importance. Peanuts are valuable as a 
substitute for cowpeas, especially in certain soils that are not adapted 
to the growing of the cowpea. In many sections where the clovers 
and other soil-renovating crops will not withstand the heat and 
drought of the summer months the peanut will thrive and make an 
excellent growth. A crop of peanuts for forage can often be grown 
after the removal of oats or some other spring crop, and although 
they may be badly overgrown by crab-grass, the tops may be mown 
with the grass for hay, and the hogs turned in to root out the peas. 

Miscellaneous Uses. The oil, beside its use as a food, is valuable 
in soap making, in lubrication and for illumination in some countries. 
The shell is often ground into a fine powder for polishing tin plate. 
It is said that tin plate manufacturers cannot get enough since this 
and middlings are the only two things that will put that mirror- 
like polish on tinware and not leave a scratch on the surface. 

Summary of Results 

The results of these investigations concerning the histology and 
physiology of Arachis present marked features which are summariz- 
ed as follows: 

I. It was found that root hairs were present on the plant, although 
reported as absent by two previous workers. These were usually 
arranged in rosettes at and on the base of side roots. Their growth 
is stimulated by a high temperature and humidity. The normally 
produced tip hairs appeared on very young plants whose roots grew 
rapidly and were exposed to moist air conditions. Later they never 
formed unless the plant showed a sudden renewal of growth vigor. 
Saturated and heavy soil conditions retarded the growth of the 
rosette type and inhibited the appearance of the tip hairs. 



336 WALDRON— THE PEANUT 

2. The hypocotyl shows a tendency to enlarge and become tuber- 
ous unless growth conditions are ideal. This is apparently due to 
a deposition of sugar from the stored food of the cotyledon which 
is unable to be cared for by the root as fast as it is supplied. 

3. The stem is quite normal. Its epidermis, however, has crystal 
cells in groups of two to four. The pith breaks down causing the 
stem to become more or less hollow. 

4. The leaf, with numerous stomata on both the upper and lower 
surfaces, has also, in both epidermal layers, small cells with a single 
contained crystal in each when young. Later these cells become 
fused into an "epidermal vessel," containing two to thirty crystals 
arranged in irregular rows or groups. 

5. The fruit stalks or gynophores have been shown to be geotropic 
in reaction, and the epidermal cells of the carpellary tips are marked- 
ly granular, suggesting a possible perceptive relation in this regard. 
These organs are very weakly hydrotropic and do not react to light 
or darkness. The epidermis of the epigeal portion has crystal cells 
like those of the stem. The epidermis of the hypogeal part becomes 
elongated in the cell walls to form absorptive hairs. The second 
layer becomes cambioid forming a phellogen-like hypodermis, and 
this, by cambioid activity, may divide into two or three layers. The 
bundles are separate and highly lignified in the outer phloem and in 
the xylem. This gives mechanical strength for soil penetration. 

6. The young fruit, as it begins to swell, bursts the epidermal and 
subjacent layers of the ovary, throwing them off. The next or third 
layer, now the pseudo-epidermis, forms irregular, more or less branch- 
ing absorptive pseudo-hairs. These are different in nature from 
any of the other hairs formed on the plant, and are indicative of the 
irregular growth of the spongy mesophyll of leaves. Beneath this 
layer are developed several zones of cells similar to, and continuous 
with, the pseudo-periderm of the gynophore. This is a marked 
peculiarity in leaf tissue formation. 

7. Attempts to produce peanuts in the air by various means 
failed to give definite results. Two succeeded by allowing the 
gynophore to grow into water; several when grown on sphagnum 
and also pure sand. None succeeded where the ovary was exposed 
to light. The results indicate that water is an important factor, 
but that contact, or darkness, or both may also be necessary. Young 
fruits, if previously in contact with soil, and then exposed to the air, 
continued to develop to a certain extent and turned green. The 



WALDRON— THE PEANUT 337 

re-formation and presence of chlorophyll in these indicate the re- 
tention through long periods of time, of factors for its formation in 
such a leaf structure. 

8. The possible benefits derived from underground fruit formation 
may be (a) protection from grazing animals, (b) formation of cer- 
tain proteins possible only in darkness, (c) more rapid and greater 
developfnent in fruit size and number. 



LITERATURE CITED 

1. Acosta. Hist. Nat. Ind., 1598. 

2. Monardes. Simpl. Med. ex Occidentali India, 1580. 

3. Marcgraf and Piso. Brazil, edit., 1648. 

4. Dubard. Une etude sur I'origine de I'arachide in Bull. Museum d'histoire nat 

urelle, n. 5, 1905. 

5. Parkinson. Theatrum Botanicum, 1640. 

6. Linnaeus. Species Plantarum. 

7. Watt. Agl. Ledger, India No. 15, 1895. 

8. Forskal. Fl. Aegypt, 1775. 

9. Delile. Fl. d.Egypt, 1824. 

ID. De Candolle. Origin of Cult. Plants, 1885. 

11. Bretschneider. Study and Value of Chinese Botanical Works, 18. 

12. Sloane. Jamaica, 1696. 

13. Rumphius. Herb. Amb., V, 1755. 

1 4. Bentham. In Flora Braziliensis, Papil. 1859. 

15. Pettit. Arachls hypogaea, Mem. Torrey Bot. Club, 4, 1895. 

16. Winton. Anatomy of the Peanut, Conn. Rept. pt. 2, 1904. 

17. Adam. L'Arachide, 1908. 

18. Richter. Beitrage zur Biologic der Arachis hypogaea, Inaug. Diss. 1899. 

19. Solereder. Anat. of Dicotyledons, V. i, 1908. 

20. Strasburger. Textbook of Botany, 1898. 

21. Jost. Plant Physiology, 1907 

22. Haberlandt. Physiological Plant Anatomy, 1914. 

23. Pfeffer. Plant Physiology, 1900. 

24. Snow. Dev. of Root Hairs. Bot. Gaz. 40, 1905. 

25. Bennett. Planting Peanuts. Ark. Bull. 58, 1899. 

26. Audouard. Development de I'arachide. Comp. Rend. 117, 5, 1893. 

27. Darwin. The Movements of Plants, 1865. 

28. Tschirch. Berichte der Deutchen Bot. Ges. 1887. 

29. Beattie. The Peanut, Farmer's Bull 431, U. S. D. A. 1917. 

Some Recent Agricultural Publications Pertaining to the Peanut 

Batten. Peanut Culture. Va. Agr. Exp. Sta. Bull. 218, 1918. 

Spencer and Jenkins. Peanuts for Oil Production, U. of Fla., Bull. 12, 1918 



-4! 




338 WALDRON— THE PEANUT 

Thompson. Peanut Growing in the Cotton Belt, S. R. S. Doc. 45, U. S. D. A., 

Ext. S., 1917. 
Duggar, Cauthen, Williamson, Sellers. Peanuts, Ala. Agri. Exp. Sta. Bull. 

193, 1917. 
Spencer and Brown. Peanuts in Florida. Univ. of Fla. Bull. 6, 191 6. 
Wolf. Leaf Spot and Some Fruit Rots of Peanut. Ala. Agr. Exp. Sta., Bull. 

180, 1914. 
Kilgore and Brown. Peanut Culture, U. Car. Dept. Agr., Vol. 30, Bull. 3, 1909. 
Jones. The Peanut Plant, 1907. 

EXPLANATION OF PLATES 
Plate LXXIX. 

Fig. 4. Root hairs (rosette type) as they appear on and at the base of side roots. 
Fig. 5. A portion of the upper epidermis of a leaf showing numerous stomata and 

crystals in "epidermal vessels." 
Fig. 6. A section through the outer layers of a peanut fruit which was about three- 
fourths grown. 

a — A portion of the epidermis and subjacent layer of the ovary 

still adhering, 
b — More or less branched fruit hairs developing from the former 

ovarian third layer, now exposed, 
c — Hypodermal tissue. 
Fig. 7. A section through the outer layers of the hypogeal part of a mature gyno- 
phore showing: 
a — Hairs formed from the epidermal layers, 
b — Two layers of the periderm-like tissue (hypoderm). 
Fig. 8. A longitudinal section through a young ovary just before the blossoming, 
a — Base of style. 
b — Pollen chamber. 

c — Enlarged and indurated cells which become the apex in Fig. 9. 
d — Ovules in ovarian cavity, 
e — Fibro-vascular bundles. 
Fig. 9. A longitudinal section through a gynophore tip, the ovary of which is three 
weeks older than that of Fig. 5, and drawn to the same scale. Note the 
very slight difference in size, the style scar at a now pushed to one 
side by the enlarged epidermal tip cells which are shown at c in Fig. 8. 

Plate LXXX. 

Fig. 10. Photo of a Spanish variety peanut plant showing flowers, flower buds and 
gynophores clustered together at its base as is typical of the Jastigiata 
subspecies. 

Fig. II. Photo of an inverted plant showing gynophores recurving in reaction to 
gravity. 

Fig. 12. Photo of plant which was righted again, shown in Fig. 11. Note the change 
of the gynophore tips again. 

Fig. 13. Photo of a plant which, after forming gynophores, was put into a moist cham- 
ber. Note the profuse development of hairs resulting. 



Bot. Contrlb. Univ. Penn. 



Vol. IV, Plate LXyiX- 




Waldron on Peanut 



Hot. Contrib. Univ. Penn. 



Vol. IV, Plate LXXX. 




Fig. 13 



Waldron on Peanut 



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